1. Field of the Invention
The present invention relates to a secondary battery having a non-aqueous electrolytic solution with a high voltage, high battery capacity and, an excellent property of charging/discharging cycle, etc.
2. Description of the Related Art
A lithium-ion secondary battery has been used, for example, in the field of portable information devices, since the battery has advantageous properties such as a high voltage (operating voltage 4.2V), high energy density, and further the demand for the battery is being increased rapidly. Nowadays, a lithium-ion secondary battery is the most popular battery for portable information devices such as a cellular phone and a laptop computer. Needless to say, as such devices are getting higher performance and more functions, it is also desired that a lithium-ion secondary battery as a power source have a higher ability (e.g., a higher capacity and a higher energy density). Varieties of technologies were proposed so as to meet this demand. For example, developments such as improvement of density with an improved filling rate of an electrode, increasing the depth of charge of an active material (especially, a negative electrode) and a new active material with high capacity, were proposed. A lithium-ion secondary battery was actually improved utilizing these technologies.
Hence, in order to attain a higher capacity, it is desired to improve an efficiency of a positive electrode active material and to develop a new high voltage material. Among them, it is brought to attention that a depth of charge of a positive electrode active material is improved by, especially, increasing a charging voltage. For example, with respect to cobalt compound oxide (LiCoO2) used as an active material for a lithium-ion battery of the 4.2V class of an operating voltage, when charging is conducted to 4.3V, with reference to a potential of Li, charging capacity is about 155 mAh/g; when being charged to 4.50V, charging capacity is about 190 mAh/g or higher. Because of such an improvement in the charging voltage, efficiency of a positive electrode active material can be improved.
However, while the capacity and an energy density of a battery are improved with higher voltage, safety and a charging/discharging cycle property of a battery tend to be lowered and further technical problems such as expansion of a battery during storage at high temperature arose.
Conventionally, the same technologies for solving such problems (e.g., the safety of a battery, low charging/discharging cycle properties and expansion of battery) were proposed. For example, in most lithium-ion secondary batteries available in the marketplace, a non-aqueous electrolytic solution includes a solvent mixture mainly composed of cyclic ester such as ethylene carbonate and linear esters such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate. It was proposed that additives such as cyclic sulfuric esters were added to a non-aqueous electrolytic solution so as to solve the above-mentioned problems of a lithium-ion secondary battery (Japanese Patent No. 3760540, Japanese laid open No. 2003-151623, Japanese laid open No. 2003-308875, Japanese laid open No. 2004-22523, Japanese Patent No. 3658506, Japanese Patent No. 3213459, Japanese Patent No. 3438636, Japanese laid open No. 9-245834, etc.).
Where a lithium-ion secondary battery, which has a non-aqueous electrolytic solution containing the additives, is charged, a dense protective film derived from the additives is formed on a surface of a negative electrode. The film continuously prevents the negative electrode from being reacted with the organic solvent in the non-aqueous electrolytic solution. Thus, after the film is formed, deterioration of battery capacity with the proceeding of charging/discharging cycle and expansion of a battery caused by gas generated in a battery can be suppressed, and a charging/discharging cycle property of battery can be improved.
Further, it is proposed that cyclic sulfone derivatives and acid anhydrides are added to non-aqueous electrolytic solution of a secondary battery such as a lithium-ion secondary battery and a primary battery so as to suppress an expansion of a battery caused by gas generated in a battery and then to provide a battery suitable for use at high temperature atmosphere. (Japanese laid open No. 2004-47413).
However, since these technologies do not provide any consideration to the technical issue in the case where an electric potential of a positive electrode can be a high voltage such as 4.35V or higher with reference to a potential of Li when a battery was fully charged, it is not sufficient to simply apply these technologies to the battery with a high voltage so as to suppress deterioration of a charging/discharging cycle character and an expansion of a battery during storage at high temperature of secondary battery.